Storage batteries which have so far been in much demand are a nickel-cadmium storage battery and a lead storage battery. However, as the use range of storage batteries have been increasing in recent years, there has been a growing request for the development of storage batteries having lighter weight, higher capacity and higher energy density. In such circumstances, intense interest has been shown towards nickel-hydrogen alkali storage batteries wherein the electrode utilizing a hydrogen absorbing alloy capable of absorbing and releasing hydrogen electrochemically is used as a negative electrode and nickel hydride is used as a positive electrode.
In such nickel-hydrogen alkali storage batteries, the hydrogen absorbing alloy electrode electrolyzes the water in an alkali electrolytic solution and absorbs the hydrogen gas produced by the electrolysis while it is being charged with electricity. During the discharge, on the other hand, the hydrogen absorbing alloy electrode releases the hydrogen gas and, at the same time, oxidizes the hydrogen gas to return it to the state of water.
When the storage battery is overcharged for the purpose of rapid charging, however, not only oxygen gas is generated from the positive electrode but also hydrogen gas is generated from the negative electrode, and thereby the internal pressure of the storage battery is increased.
This is being the case, it has been proposed to design the negative electrode so as to have a greater chargeable capacity than the positive electrode, thereby preferentially generating oxygen gas upon charging. Therein, the oxygen gas generated is made to react with the hydrogen gas produced on the negative electrode to be converted into water; as a result, a rise in the internal pressure of the storage battery can be controlled.
An increase in the chargeable capacity of the negative electrode, although it can inhibit the increase in an internal pressure of the battery upon overcharging, has a defect that it requires a correlative decrease in the volume occupied by the positive electrode in the storage battery to result in the lowering of the battery capacity (per volume capacity).
By our intensive studies with the intention of obviating such a defect, it has already been found and disclosed in Japanese Tokkai Hei 9-97605 (wherein the term "Tokkai" as used herein means an "unexamined published patent application") that, when the surface of a hydrogen absorbing alloy electrode is coated with a fluorine-containing water repellent agent, no surface of the electrode is wetted with an electrolytic solution and a three-phase interface of gas, liquid and solid is formed thereon, and thereby not only the hydrogen gas absorbing properties of the electrode can be improved but also no increase of internal pressure is caused in the storage battery even when the storage battery undergoes rapid charging to result in extension of charge-discharge cycle life, and further an increase in chargeable capacity of the negative electrode can be reduced to the minimum to result in prevention of drop in battery capacity.